The present invention relates to a cemented carbide cutting tool insert, particularly useful for turning, milling and drilling in steels and stainless steels.
Conventional cemented carbide inserts are produced by powder metallurgical methods including milling of a powder mixture forming the hard constituents and the binder phase, pressing and sintering. The milling operation is an intensive milling in mills of different sizes and with the aid of milling bodies. The milling time is of the order of several hours up to several days. Such processing is believed to be necessary in order to obtain a uniform distribution of the binder phase in the milled mixture. It is further believed that the intensive milling causes reactivity of the mixture which further promotes the formation of a dense structure. However, milling has its disadvantages. During the long milling time the milling bodies are worn and contaminate the milled mixture. Furthermore even after an extended milling a random rather than an ideal homogeneous mixture may be obtained. Thus, the properties of the sintered cemented carbide containing two or more components depend heavily on how the starting materials are mixed.
There exist alternative technologies to intensive milling for production of cemented carbide. For example, particles can be coated with binder phase metal. The coating methods include fluidized bed methods, solgel techniques, electrolytic coating, PVD coating or other methods such as disclosed in e.g. GB 346,473, U.S. Pat. Nos. 5,529,804 or 5,505,902. Coated carbide particles can be mixed with additional amounts of cobalt and other carbide powders to obtain the desired final material composition, pressed and sintered to form a dense structure. U.S. Pat. No. 5,993,730 discloses a method of coating carbide particles with V, Cr, Ti, Ta or Nb.
During metal cutting operations like turning, milling and drilling the general properties of the material such as hardness, resistance against plastic deformation, and resistance against formation of thermal fatigue cracks are to a great extent related to the volume fraction of the hard phases and the binder phase in the sintered cemented carbide body. It is well known that increasing the amount of the binder phase reduces the resistance to plastic deformation. Different cutting conditions require different properties of the cutting insert. When cutting in steels with raw surface zones (e.g. rolled, forged or cast) a coated cemented carbide insert must consist of tough cemented carbide and have a very good coating adhesion as well. When turning, milling or drilling in low alloyed steels or stainless steels the adhesive wear is generally the dominating wear type.
Measures can be taken to improve the cutting performance with respect to a specific wear type. However, such action will often have a negative effect on other wear properties.